The research goal for the coming year will be a comparative study of the Mo-MCF/Mo-MuLV system inducing thymus-derived lymphomas and the Rauscher (R)-MCF/R-MuLV system inducing erythroblastomas. A (R)-MCF virus was recently isolated in this laboratory and is most likely analogous to the Friend (FR)-MCF virus isolated by Troxler et al. (J. Exp. Med., 148, 639-653, 1978) from spleens of NIH Swiss mice that had been injected with high doses of ecotropic (FR)-MuLV.